Multitrack optical disc reader

ABSTRACT

A multitrack optical disc reader ( 1 ) is disclosed comprising a multitrack optical pick up ( 11 ) for reading data from multiple tracks of an optical disc ( 10 ) and outputting the data from each track in respective data streams, and multiple first-in-first-out (FIFO) memories ( 21 ) for temporarily storing the data streams. In accordance with the present invention, wherein the pickup may selectively output data streams from less than the maximum number of tracks that can be read by the pickup, the multiple FIFO memories are provided in a common memory bank, and when less than the maximum number of tracks are being read by the pickup, the size of at least one FIFO memory in use is greater than the total available FIFO memory in the common memory bank divided by the maximum number of tracks that can be read by the pickup.

This invention relates to a multitrack optical disc reader comprising amultitrack optical pick up for reading data from multiple tracks of anoptical disc and outputting the data from each track in respective datastreams, and first-in-first-out (FIFO) buffers for temporarily storingdata from the respective data streams.

FIG. 1 shows, schematically, a conventional optical disc reader 1comprising a multitrack optical pick up 11 for reading data from fiveadjacent tracks of an optical disc 10 and outputting the data read fromeach track in five data streams. Each data stream is fed in to anintegrated circuit 12 in which the data streams are combined and thecombined data decoded. Specifically, each data stream is fed in to frontend (FE) processing circuitry 13 where bit data is recovered anddemodulated, and this data is then temporarily stored in a FIFO buffer14. From the FIFO buffers, the data streams are combined using amultiplexer 15 and the combined data stored in a fast access, SDRAMmemory 18 located off-chip. Decoding circuitry 17 located on theintegrated circuit retrieves and decodes the combined data stored in theSDRAM memory 18 and feeds the decoded data to an output 20, for example,as a video or audio stream. The FE processing circuitry, FIFO buffers,multiplexer and decoder are all control by a microcontroller (μC) 16which in turn is controlled by an off-chip central processing unit (CPU)19.

The temporarily storage of data streams in FIFO buffers enables data tobe written from the FIFO buffers to the SDRAM memory in bursts which isnecessary if the fast access, SDRAM memory is to be written toefficiently. Unfortunately, hardwired FIFOs buffers substantiallyincrease the gate count of any integrated circuit which contains them,and therefore there is a trade off between using small FIFOs, i.e. a lowgate count, and achieving fast memory access.

According to the present invention, a multitrack optical disc reader ofthe aforementioned type is provided with a memory bank in which the FIFObuffers may be dynamically defined.

Where the disc reader is able to use and is using less than the maximumnumber of tracks that can be read by the pickup, as is common, thepresent invention enables at least one of the FIFO buffers to be definedto have a size greater than would otherwise be the case. That is,greater than the total FIFO memory that can be defined in the memorybank divided by the maximum number of tracks that can be read by thepickup. For any given amount of FIFO memory (and associated gate count),larger FIFOs are used and thus larger bursts of data can be subsequentlywritten to fast access memory, thereby increasing the efficiency of thesame.

Also, only FIFO buffers for data streams for those tracks used need tobe defined and where this is the case, each of the FIFO buffers may bedefined to has a size equal to the total FIFO memory divided by thenumber of tracks being used. That is, the available FIFO memory isshared equally amongst the tracks in use.

The present invention will now be described, by way of example only,with reference to the accompanying schematic drawings in which:

FIG. 1 shows, schematically, a conventional multitrack optical discreader as hereinbefore described;

FIG. 2 shows, schematically, a multitrack optical disc reader inaccordance with the present invention;

FIG. 3 illustrates the mapping of buffered data stored in theconventional disc reader of FIG. 1 compared to that of the disc readerof the present invention of FIG. 2.

The same reference signs are used to refer to corresponding or similarfeatures in both the conventional multitrack optical disc reader of FIG.1 and the multitrack optical disc reader of FIG. 2 according to thepresent invention.

Referring to FIG. 2, an optical disc reader 1 is shown comprising allthe features of the multitrack optical disc reader of FIG. 1 except thatthe disc reader is able to use less than the maximum number of tracksthat can be read by the pickup. Also, in accordance with the presentinvention, the FIFO buffers are may be dynamically defined in a commonmemory bank 21.

For the purposes of illustration, suppose only the inner, outer andmiddle tracks of the 5 track optical pick up are being used and thusonly data from those tracks is being streamed to the integrated circuit12 where the data streams are combined and the combined data decoded. Astwo out of 5 tracks are not being used, 3 equally sized FIFO buffers maybe defined in the memory bank 21 of a size two thirds greater than wouldbe the case if all five tracks were being used. Therefore, anysubsequent data burst transferring data from the FIFO buffers to thefast access, SDRAM memory 18 located off-chip can be two thirds greater,thereby increases the efficiency of this transfer and, with the transferbeing under the control of microcontroller (μC) 16, so reducing the loadon the CPU 19.

This increase FIFO size is illustrated in FIG. 3 which maps availableFIFO buffered data stored in the conventional disc reader of FIG. 1 whenall 5 tracks (labelled 1 to 5) are in use to that of the disc reader ofthe present invention of FIG. 2 when only inner, outer and middle tracksare in use (tracks 1, 3 and 5).

In the above described examples of a conventional multitrack opticaldisc reader and one in accordance with the present invention, the fastaccess SDRAM memory is located off-chip though, of course, this couldalso be another type of memory and/or integrated with the FE circuitry,FIFO buffers, multiplexer and decoder on the integrated circuit.

From reading the present disclosure, other modifications will beapparent to persons skilled in the art. Such modifications may involveother features which are already known in the design and use ofmultitrack optical disc drives and component parts thereof and which maybe used instead of or in addition to features already described herein,and at least including those features described in U.S. Pat. Nos.5,793,549, 5,907,526, 5,959,953, 6,028,827 and 6,216,201.

1. A multitrack optical disc reader comprising: a multitrack opticalpick up for reading data from multiple tracks of an optical disc andoutputting data from each track in respective data streams; and a memorybank in which first-in-first-out (FIFO) buffers for temporarily storingdata from the respective data streams may be dynamically defined,wherein the reader can use less than the maximum number of tracks thatcan be read such that when less than the maximum number of tracks thatcan be read are being used, one or more of the FIFO buffers are definedto have a size equal to or greater than the total FIFO memory that canbe defined in the memory bank divided by the number of tracks that canbe read being used or the maximum number of tracks that can be read bythe pickup.